The present invention relates to process flow control, and particularly to a parallel control method for sequential process control flow of equipment automation.
The process control flow of equipment automation follows a series of pre-defined steps to process products, such as on lot-based wafers in a foundry, to ensure that wafers are processed in a correct sequence of steps or operations. The flow starts as FOUP (carrier) loaded on equipment and terminates as FOUP unloaded from equipment. Each pre-defined step performs specific operations on equipment, MES (Manufacturing Execution System) or other related servers. The basic steps include steps, such as “AskReadLotTag” to read the smart tag of FOUP, “LotVerfy” to verify the status of lots in FOUP with MES, “AskProceedWithCarrier” to ask equipment to dock FOUP, “OperationStart” and “OperationComplete” to track in and track out FOUP with MES, “AskStartProcess” to create jobs on equipment for wafer processing on lot-based, and some enhancement steps.
FIG. 1 illustrates an example of a sequential process control flow 100 in wafer fabrication. In the example, the sequential process control flow 100 has 12 steps including “AskReadLotTag”, “LotVerfy”, “EQPStatusCheck”, “RMSCheck”, “ECSCheck”, “PMSCheck”, “AskProceedWithCarrier”, “ReportDockComplete”, “ReportSlotMap”, “AskWriteLotTag”, “OperationStart”, and “AskStartProcess”, respectively. A step can be executed only when the previous one is completed normally or skippable. For example, the “AskStartProcess” step can be performed only when FOUP is tracked in with MES successfully. Thus, the process control flow of equipment automation is a sequential flow composed of several distinct steps according to the behavior of equipment and the process requirements.
The major advantage of such sequential flow is to guarantee wafers are processed by definite order of steps or operations without errors. Generally, when FOUP is processed by a step, it implies that the steps before it have all been completed normally. If an exception occurs in that step, such sequential flow can guarantee that the steps before it are all executed completely and determine a proper procedure to recover or resolve the issue after exception. For example, if an exception occurs in the “OperationComplete” step, it implies that FOUP is already tracked in MES and processed by equipment. Therefore, the exception handling procedure of this step is first undocking FOUP and keeping FOUP on load port and then sending an alarm to inform related personnel for subsequent handling. Besides, such sequential flow allows only one step or operation to execute in one time. This behavior can guarantee the execution of each step is in a controllable and traceable state. If exception occurs in a step, it can be handled immediately without waiting to ensure the safety of the wafer processing. For example, if at least two steps are executing in the same time by the technology of multi-thread, exceptions in a step is hard to be handled immediately because it doesn't have proper timing to synchronize all the status of the steps in executing at that moment. When all the steps finish execution, the process control flow might be out of control and lead to miss operation if exceptions are not recorded correctly. Such concerns can be solved easily in a sequential process control flow.
The major disadvantage of current process control flow, however is long processing time for the entire sequential process control flow, and the extended processing time for a FOUP on equipment when a new step or operation is added to the process control flow. For example, if a new APC (Advanced Process Control) step or operation which takes 10 seconds to complete is added into a current photo process control flow, photo equipment processing time is extended by exactly 10 seconds for a FOUP. Thus, a process control flow performance suffers when additional steps or operations are added.